Degenerative feedback amplifier



1, 1940- L. w. MEYER 2,216,516

' DEGENERATIVE FEEDBACK AMPLIFIER Filed Nov. 16, 195',

' f 2 Le LOAD m smn/cs SIG/IA; SOURCE}? 5 M A 5 R 1 5 lNVENTOl-Q LESLIE IV. EVER BY MK ATTORNEY Patented Oct. 1, 1940 UNITED STATES PATENT OFFICE DEGENERATIVE FEEDBACK AMPLIFIER Delaware Application November 16, 1937, Serial No. 174,769 In Great Britain April 2, 1937 1 Claim.

This invention relates to thermionic amplifiers of the so-called degenerative type, i. e. amplifiers in which there is a negative feed-back from the anode circuit of an amplifying valve to the grid circuit of the same valve or a preceding valve. It is, more particularly, concerned with amplifiers of the kind in which this negative feed-back is obtained by means of a resistance or other impedance included in the cathode lead of the valve.

According to the present invention, in an amplifier of the kind just specified the valve utilized is a valve having a suppressor grid interposed between a screening grid and an anode, e. g. suppressorgrid pentode, and the suppressor grid is con- 15 nected either to that end of the feed-back impedance in the cathode lead which is remote from the cathode, or to a point intermediate the ends of said impedance. This connection may be a permanent one, or it may be variable. If with such an arrangement the anode impedance of the valve is a resistance, the suppressor grid potential will fluctuate in phase with the anode potential,

i. e., the negative bias on the suppressor grid will increase when the anode potential falls.

One embodiment is shown by way of example in the accompanying drawing, wherein V designates a suppressor-grid pentode supplied with the signal to be amplified by way of an input circuit,

diagrammatically shown as a source of voltage S,

30 connected between the control grid 1 and the lower end of a resistance R in the cathode lead.

The screening grid 2 is connected through a condenser C to the cathode, and through a resistance R1 to a suitable source of positive potential.

35 The anode 3 is connected through a load impedance Z (e. g. a resistance) to the same or a different source of positive potential, the said source, or sources, at the negative end being connected to the lower end of resistance R. According to the invention the suppressor grid 4 is connected either to the lower end of the resistance R, or to a tapping intermediate the ends of the 5 said resistance. This connection may be of a fixed or variable character. The variable tap 5 permits the point of connection to resistor R to be chosen. The purpose of connecting grid 4 to some point of resistor R remote from the cathode is to put a larger negative potential on grid 4 when the amplitude of the negative signal peaks on the anode 3 get larger. This insures that the potential of the suppressor grid will always be lower than that of the anode, even at those instants when said negative peaks occur.

What is claimed is:

In a signal amplifier circuit, a tube of the type provided with at least a cathode, signal grid, a plate and an auxiliary cold electrode located between the signal grid and plate, an unby-passed resistor connected between said cathode and a point of fixed potential and developing thereacross a direct current voltage by virtue of the tubespace current flow therethrough, a source of signals connected between the signal grid and said point whereby signal voltage is developed across said resistor, the entire direct current voltage across said resistor being applied to the signal grid as a negative bias, the entire signal voltage across said resistor being applied in degenerative phase to said signal grid, and an adjustable connection between said auxiliary cold electrode and said resistor for providing a path of variable negative bias and adjustable degenerative signal voltage feed-back to said auxiliary cold electrode.

LESLIE WILLIAM MEYER. 

